The aim of wheel slip control such as ABS (Anti-lock Braking System) or TCS (Traction Control System) is to control or limit braking slip or drive slip occurring on wheels to an optimal slip. An optimal braking slip amounts to e.g. 12%. The wheel slip is determined by comparing the wheel speed of the wheel involved with a central reference speed. The measured wheel slip also contains, apart from the components longitudinal slip and braking slip or drive slip, which should be controlled within the scope of ABS or TCS, a component that arises when traversing a turn, as the wheels on the outside of the turn rotate faster than the wheels on the inside of the turn. Said turn slip component consists of the difference in revolution rates between the wheels when turning and depends on the position of the wheels on the vehicle (front/rear; left/right), on the turn radius, on the geometry of the vehicle and on the speed of the vehicle. Because of the information originating exclusively from the wheel revolution rate sensors, the ABS or the TCS does not “know” in such cases whether the measured difference in revolution rates between the wheels is caused by different coefficients of friction (μ-split) of the wheels or by turning.
In order to compensate the difference in revolution rates between the wheels in a turn during braking slip control (ABS), according to the prior art, the difference in revolution rates between the wheels prior to braking is observed and is taken into account when determining the braking slip in braking situations. Such compensation of the difference in revolution rates between the wheels during ABS in a turn is e.g. discussed in DE 42 01 675 C1 or DE 195 22 634 A1.
If, however, the turn radius changes during braking, e.g. if the driver changes the steering angle with the vehicle already in a turn, then the difference in revolution rates between the wheels is no longer compensated exactly. Above all, in the case of small brake slip during ABS control the percentage error arising from the differences in revolution rates can be very large.